1、添加easyExcel相关依赖

		<dependency>
            <groupId>org.apache.poi</groupId>
            <artifactId>poi</artifactId>
            <version>5.2.2</version>
        </dependency>
        <dependency>
            <groupId>org.apache.poi</groupId>
            <artifactId>poi-ooxml</artifactId>
            <version>5.2.2</version>
        </dependency>
        <dependency>
            <groupId>org.apache.poi</groupId>
            <version>5.2.2</version>
            <artifactId>poi-ooxml-lite</artifactId>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.13.2</version>
        </dependency>
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>easyexcel</artifactId>
            <version>3.2.1</version>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>1.18.22</version>
        </dependency>
        <dependency>
            <groupId>cn.hutool</groupId>
            <artifactId>hutool-all</artifactId>
            <version>5.8.12</version>
        </dependency>

2、准备基础工具类

DemoData .class

@Getter
@Setter
@EqualsAndHashCode
public class DemoData {
    @ExcelProperty("字符串标题")
    private String string;
    @ExcelProperty("日期标题")
    private Date date;
    @ExcelProperty("数字标题")
    private Double doubleData;
    /**
     * 忽略这个字段
     */
    @ExcelIgnore
    private String ignore;
}

TestFileUtil.class

public class TestFileUtil {


    public static InputStream getResourcesFileInputStream(String fileName) {
        return Thread.currentThread().getContextClassLoader().getResourceAsStream("" + fileName);
    }

    public static String getPath() {
        return TestFileUtil.class.getResource("/").getPath();
    }

    public static File createNewFile(String pathName) {
        File file = new File(getPath() + pathName);
        if (file.exists()) {
            file.delete();
        } else {
            if (!file.getParentFile().exists()) {
                file.getParentFile().mkdirs();
            }
        }
        return file;
    }

    public static File readFile(String pathName) {
        return new File(getPath() + pathName);
    }

    public static File readUserHomeFile(String pathName) {
        return new File(System.getProperty("user.home") + File.separator + pathName);
    }
}

3、创建水印handler类

WaterMarkHandler.class水印生成类
EasyExcel提供了一个水印接口类，我们实现SheetWriteHandler自定义我们的水印

@RequiredArgsConstructor
public class WaterMarkHandler implements SheetWriteHandler {

    private final String WATER_MARK;

    public static ByteArrayOutputStream createWaterMark(String content) throws IOException {
        int width = 200;
        int height = 150;
        BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);// 获取bufferedImage对象
        String fontType = "微软雅黑";
        int fontStyle = Font.BOLD;
        int fontSize = 20;
        Font font = new Font(fontType, fontStyle, fontSize);
        Graphics2D g2d = image.createGraphics(); // 获取Graphics2d对象
        image = g2d.getDeviceConfiguration().createCompatibleImage(width, height, Transparency.TRANSLUCENT);
        g2d.dispose();
        g2d = image.createGraphics();
        g2d.setColor(new Color(0, 0, 0, 20)); //设置字体颜色和透明度，最后一个参数为透明度
        g2d.setStroke(new BasicStroke(1)); // 设置字体
        g2d.setFont(font); // 设置字体类型 加粗 大小
        g2d.rotate(-0.5, (double) image.getWidth() / 2, (double) image.getHeight() / 2);//设置倾斜度
        FontRenderContext context = g2d.getFontRenderContext();
        Rectangle2D bounds = font.getStringBounds(content, context);
        double x = (width - bounds.getWidth()) / 2;
        double y = (height - bounds.getHeight()) / 2;
        double ascent = -bounds.getY();
        double baseY = y + ascent;
        // 写入水印文字原定高度过小，所以累计写水印，增加高度
        g2d.drawString(content, (int) x, (int) baseY);
        // 设置透明度
        g2d.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_OVER));
        // 释放对象
        g2d.dispose();
        ByteArrayOutputStream os = new ByteArrayOutputStream();
        ImageIO.write(image, "png", os);
        return os;
    }

    /**

     为Excel打上水印工具函数
     @param sheet excel sheet
     @param bytes 水印图片字节数组
     */
    public static void putWaterRemarkToExcel(SXSSFSheet sheet, byte[] bytes) {
        //add relation from sheet to the picture data
        SXSSFWorkbook workbook = sheet.getWorkbook();
        XSSFSheet shReflect = (XSSFSheet) ReflectUtil.getFieldValue(sheet, "_sh");
        int pictureIdx = workbook.addPicture(bytes, Workbook.PICTURE_TYPE_PNG);
        XSSFPictureData xssfPictureData = (XSSFPictureData) workbook.getAllPictures().get(pictureIdx);
        PackagePartName ppn = xssfPictureData.getPackagePart().getPartName();
        PackageRelationship pr = shReflect.getPackagePart().addRelationship(ppn, TargetMode.INTERNAL, XSSFRelation.IMAGES.getRelation(), null);
        //set background picture to sheet
        shReflect.getCTWorksheet().addNewPicture().setId(pr.getId());
    }
    @Override
    public void beforeSheetCreate(WriteWorkbookHolder writeWorkbookHolder, WriteSheetHolder writeSheetHolder) {
    }

    @SneakyThrows
    @Override
    public void afterSheetCreate(WriteWorkbookHolder writeWorkbookHolder, WriteSheetHolder writeSheetHolder) {
        try (ByteArrayOutputStream waterMark = createWaterMark(WATER_MARK)){
            SXSSFSheet sheet = (SXSSFSheet) writeSheetHolder.getSheet();
            putWaterRemarkToExcel(sheet, waterMark.toByteArray());
        }
    }
}

4、创建单元测试类WriteTest.class

public class WriteTest {

    @Test
    public void writer() {
        String fileName = TestFileUtil.getPath() + "simpleWrite" + System.currentTimeMillis() + ".xlsx";
        // 这里 需要指定写用哪个class去写，然后写到第一个sheet，名字为模板 然后文件流会自动关闭
        // 如果这里想使用03 则 传入excelType参数即可
        EasyExcel.write(fileName, DemoData.class)
                .registerWriteHandler(new WaterMarkHandler("zhangsan"))
                .sheet("模板")
                .doWrite(() -> {
                    // 分页查询数据
                    return data();
                });
    }

    private List<DemoData> data() {
        List<DemoData> list = ListUtils.newArrayList();
        for (int i = 0; i < 10; i++) {
            DemoData data = new DemoData();
            data.setString("字符串" + i);
            data.setDate(new Date());
            data.setDoubleData(0.56);
            list.add(data);
        }
        return list;
    }
}

5、测试结果

导出的excel成功添加水印